Abstract:

Aspects of the invention are directed to systems and method for limiting
losses in an uninterruptible power supply. In one aspect, the present
invention provides an uninterruptible power supply (UPS) comprising an
input to receive input power having an input voltage, an output to
provide output power having an output voltage, a neutral line, an
automatic voltage regulation (AVR) transformer coupled to the input and
the output of the UPS and having an input, an output, a core and at least
one switch controllably coupled to at least one of the core, the input
and the output, and a means for isolating the core of the AVR transformer
from the neutral line when the input voltage is substantially equal to a
defined output voltage.

Claims:

1. An uninterruptible power supply (UPS) system comprising:an input to
receive input power having an input voltage;an output to provide output
power;a neutral line;an automatic voltage regulation (AVR) transformer
coupled to the input and the output of the UPS and having an input, an
output, a core and at least one switch controllably coupled to at least
one of the core, the input and the output;a bypass switch configured to
selectively couple the core of the AVR transformer to the neutral line;
anda controller configured to control the at least one switch of the AVR
transformer and the bypass switch,wherein the controller is configured to
control the bypass switch to isolate the core of the AVR transformer from
the neutral line in a first mode of operation and to couple the core of
the AVR transformer to the neutral line in a second mode of operation.

2. The system of claim 1, wherein the controller is configured to, in the
first mode of operation, couple the at least one switch of the AVR
transformer to the core and to at least one of the AVR transformer input
and the AVR transformer output in a configuration to provide an output
voltage of the AVR transformer that is equal to an input voltage of the
AVR transformer.

3. The system of claim 2, further comprising a DC voltage source and an
inverter coupled to the DC voltage source, wherein the inverter is
coupled to the input of the AVR transformer and is configured to provide
regulated AC power to the AVR transformer.

4. The system of claim 3, wherein the DC voltage source includes a
battery.

5. The system of claim 1, wherein the controller is configured to, in the
second mode of operation, couple the at least one switch of the AVR
transformer to the core and to at least one of the AVR transformer input
and the AVR transformer output in a configuration to provide an output
voltage of the AVR transformer that is greater than an input voltage of
the AVR transformer by a first ratio.

6. The system of claim 5, wherein the controller is configured, in a third
mode of operation, to control the bypass switch to couple the core of the
AVR transformer to the neutral line and wherein the controller is further
configured to couple the at least one switch of the AVR transformer to
the core and to at least one of the AVR transformer input and the AVR
transformer output in a configuration to provide an output voltage of the
AVR transformer that is greater than the input voltage of the AVR
transformer by a second ratio which is larger than the first ratio.

7. The system of claim 6, wherein the second ratio is twice the first
ratio.

8. The system of claim 5, wherein the controller is configured, in a
fourth mode of operation, to control the bypass switch to couple the core
of the AVR transformer to the neutral line and wherein the controller is
further configured to couple the at least one switch of the AVR
transformer to the core and to at least one of the AVR transformer input
and the AVR transformer output in a configuration to provide an output
voltage of the AVR transformer that is less than the input voltage of the
AVR transformer.

9. The system of claim 1, wherein the bypass switch is an electromagnetic
switch.

10. The system of claim 9, wherein the electromagnetic switch is a relay.

11. The system of claim 10, wherein the relay is a single pole double
throw relay.

12. The system of claim 10, wherein the relay is a single pole single
throw relay.

13. A method of providing stable power in an uninterruptible power supply
(UPS) having an automatic voltage regulation (AVR) transformer, an input
to receive input power having an input voltage with an AC voltage
waveform, an output to provide output power having an output voltage, and
a neutral line, the AVR transformer having an input, an output and a core
selectively coupled to the neutral line, the method
comprising:determining whether the input voltage to the UPS is within a
specified tolerance;if the input voltage to the UPS satisfies a first
condition, isolate the core of the AVR transformer from the neutral line;
andif the input voltage of the UPS satisfies a second condition, couple
the core of the AVR transformer to the neutral line.

14. The method of claim 13, further comprising acts of:configuring the AVR
transformer to boost the output voltage of the UPS if the input voltage
of the UPS is less than a specified tolerance; andconfiguring the AVR
transformer to reduce the output voltage of the UPS if the input voltage
of the UPS is greater than a specified tolerance.

15. The method of claim 13, wherein the act of isolating comprises an act
of decoupling the core of the AVR transformer from the neutral line.

16. The method of claim 13, wherein the AVR transformer includes at least
one switch controllably coupled to at least one of the core, the input of
the AVR transformer and the output of the AVR transformer, and a bypass
switch configured to selectively couple the core of the AVR transformer
to the neutral line,wherein the act of isolating further comprises an act
of coupling the at least one switch to the core and one half cycle later,
controlling the bypass switch to decouple the core from the neutral
line,wherein the act of coupling the core to the neutral line further
comprises an act of controlling the bypass switch to couple the core to
the neutral line and one half cycle later, coupling the at least one
switch to the core.

17. The method of claim 16, wherein the act of controlling the bypass
switch to decouple the core from the neutral line comprises an act of
energizing the bypass switch at a zero crossing of the AC voltage
waveform,wherein the act of controlling the bypass switch to couple the
core to the neutral line comprises an act of energizing the bypass switch
at a zero crossing of the AC voltage waveform.

18. An uninterruptible power supply (UPS) system comprising:an input to
receive input power having an input voltage;an output to provide output
power having an output voltage;a neutral line;an automatic voltage
regulation (AVR) transformer coupled to the input and the output of the
UPS and having an input, an output, a core and at least one switch
controllably coupled to at least one of the core, the input and the
output; andmeans for isolating the core of the AVR transformer from the
neutral line when the input voltage is substantially equal to a defined
output voltage.

19. The system of claim 18, wherein the at least one switch is selectively
coupled, in a first mode of operation, to the core in a configuration to
provide an output voltage of the AVR transformer that is equal to an
input voltage of the AVR transformer.

20. The system of claim 19, further comprising a DC voltage source coupled
to an inverter and wherein the inverter is coupled to the AVR transformer
and is configured to provide regulated AC power to the AVR transformer.

21. The system of claim 20, wherein the DC voltage source includes a
battery.

22. The system of claim 18, wherein, in a second mode of operation, the
core of the AVR transformer is coupled to the neutral line and the at
least one switch is selectively coupled to the core in a configuration
that results in the output voltage of the AVR transformer being greater
than the input voltage of the AVR transformer by a first ratio.

23. The system of claim 18, wherein, in a third mode of operation, the
core of the AVR transformer is coupled to the neutral line and the at
least one switch is selectively coupled to the core in a configuration
that results in the output voltage of AVR transformer to be greater than
the input voltage of the AVR transformer by a second ratio which is
larger than the first ratio.

24. The system of claim 23, wherein the second ratio is twice the first
ratio.

25. The system of claim 18, wherein, in a fourth mode of operation the
core of the AVR transformer is coupled to the neutral line and the at
least one switch is selectively coupled to the core in a configuration
that results in the output voltage of the AVR transformer being smaller
than the input voltage of the AVR transformer.

Description:

BACKGROUND OF INVENTION

[0001]1. Field of Invention

[0002]At least one embodiment of the invention relates generally to a
method and system for providing uninterruptible, regulated power to
critical and/or sensitive loads. More specifically, at least one
embodiment of the invention relates to the reduction of losses in an
uninterruptible power supply due to an automatic voltage regulation
transformer.

[0003]2. Discussion of Related Art

[0004]The use of an uninterruptible power system (UPS) to provide power to
a critical load is known. Known uninterruptible power systems include
on-line UPS's, off-line UPS's, line interactive UPS's as well as others.
On-line UPS's provide conditioned AC power as well as back-up AC power
upon interruption of a primary source of AC power. Off-line UPS's
typically do not provide conditioning of input AC power, but do provide
back-up AC power upon interruption of the primary AC power source. Line
interactive UPS's are similar to off-line and on-line UPS's in that they
still switch to battery power when a blackout occurs; however, when a
power line sag or swell occurs, at least one type of line interactive UPS
activates a tap switching voltage regulation circuit to stabilize the
output voltage continuously, without consuming battery power. This allows
equipment connected to the UPS to continue to operate through extended
power line sags or swells without draining the battery. The tap switching
voltage regulation circuit often includes an automatic voltage regulation
(AVR) transformer.

SUMMARY OF THE INVENTION

[0005]In embodiments of the present invention, the problems associated
with AVR transformer energy loss in a UPS are reduced by de-energizing
the core of the transformer and preventing losses due to the AVR
transformer when the AVR is not performing a regulation function.

[0006]In one aspect, the present invention features an uninterruptible
power supply (UPS). The UPS may include an input to receive input power
having an input voltage, an output to provide output power, a neutral
line, and an automatic voltage regulation (AVR) transformer coupled to
the input and the output of the UPS, the AVR transformer having an input,
an output, a core, and at least one switch controllably coupled to at
least one of the core, the input and the output. The UPS further
comprises a bypass switch configured to selectively couple the core of
the AVR transformer to the neutral line, and a controller configured to
control the at least one switch of the AVR transformer and the bypass
switch, wherein the controller is configured to control the bypass switch
to isolate the core of the AVR transformer from the neutral line in a
first mode of operation and to couple the core of the AVR transformer to
the neutral line in a second mode of operation.

[0007]According to one or more aspects of the invention, the controller is
configured to, in the first mode of operation, couple the at least one
switch of the AVR transformer to the core and to at least one of the AVR
transformer input and the AVR transformer output in a configuration to
provide an output voltage of the AVR transformer that is equal to an
input voltage of the AVR transformer.

[0008]According to one or more aspects of the invention, the UPS further
comprises a DC voltage source and an inverter coupled to the DC voltage
source, wherein the inverter is coupled to the input of the AVR
transformer and is configured to provide regulated AC power to the AVR
transformer. Also, according to one or more aspects of the invention, the
DC voltage source includes a battery.

[0009]According to one or more aspects of the invention, the controller is
configured to, in the second mode of operation, couple the at least one
switch of the AVR transformer to the core and to at least one of the AVR
transformer input and the AVR transformer output in a configuration to
provide an output voltage of the AVR transformer that is greater than an
input voltage of the AVR transformer by a first ratio.

[0010]According to one or more aspects of the invention, the controller is
configured, in a third mode of operation, to control the bypass switch to
couple the core of the AVR transformer to the neutral line and wherein
the controller is further configured to couple the at least one switch of
the AVR transformer to the core and to at least one of the AVR
transformer input and the AVR transformer output in a configuration to
provide an output voltage of the AVR transformer that is greater than the
input voltage of the AVR transformer by a second ratio which is larger
than the first ratio. Also, according to one or more aspects of the
invention, the second ratio may be twice the first ratio.

[0011]According to one or more aspects of the invention, the controller is
configured, in a fourth mode of operation, to control the bypass switch
to couple the core of the AVR transformer to the neutral line and wherein
the controller is further configured to couple the at least one switch of
the AVR transformer to the core and to at least one of the AVR
transformer input and the AVR transformer output in a configuration to
provide an output voltage of the AVR transformer that is less than the
input voltage of the AVR transformer by a third ratio. According to one
or more aspects of the invention, the third ratio may be 1.15:1. Also,
according to one or more aspects of the invention, the bypass switch is
an electromagnetic switch. In addition, according to one or more aspects
of the invention, the electromagnetic switch is a relay. According to one
or more aspects of the invention, the relay is a single pole double throw
relay or a single pole single throw relay.

[0012]In another aspect, the present invention features a method of
providing stable power in an uninterruptible power supply (UPS) having an
automatic voltage regulation (AVR) transformer, an input to received
input power having an input voltage, an output to provide output power
having an output voltage, and a neutral line, the AVR transformer having
an input, an output and a core selectively coupled to the neutral line,
the method comprising determining whether the input voltage to the UPS is
within a specified tolerance, if the input voltage to the UPS satisfies a
first condition, isolate the core of the AVR transformer from the neutral
line and if the input voltage of the UPS satisfies a second condition,
couple the core of the AVR transformer to the neutral line.

[0013]According to one or more aspects of the method, the method further
comprises the act of configuring the AVR transformer to boost the output
voltage of the UPS if the input voltage of the UPS is less than a
specified tolerance and configuring the AVR transformer to reduce the
output voltage of the UPS if the input voltage of the UPS is greater than
a specified tolerance.

[0014]According to one or more aspects of the method; the act of isolating
comprises an act of decoupling the core of the AVR transformer from the
neutral line.

[0015]According to one or more aspects of the method, the method further
includes at least one switch controllably coupled to at least one of the
core, the input of the AVR transformer and the output of the AVR
transformer, and a bypass switch configured to selectively couple the
core of the AVR transformer to the neutral line, wherein the act of
isolating further comprises the act of coupling the at least one switch
to the core and one half cycle later, controlling the bypass switch to
decouple the core from the neutral line, wherein the act of coupling the
core to the neutral line further comprises the act of controlling the
bypass switch to couple the core to the neutral line and one half cycle
later, coupling the at least one switch to the core.

[0016]In another aspect, the present invention features a UPS. The UPS
having an input to receive input power having an input voltage, an output
to provide output power having an output voltage, a neutral line, and an
AVR transformer coupled to the input and the output of the UPS and having
an input, an output, a core and at least one switch controllably coupled
to at least one of the core, the input and the output. The UPS further
comprises a means for isolating the core of the AVR transformer from the
neutral line when the input voltage is substantially equal to a defined
output voltage.

[0017]According to one or more aspects of the invention, the at least one
switch is selectively coupled, in a first mode of operation, to the core
in a configuration to provide an output voltage of the AVR transformer
that is equal to an input voltage of the AVR transformer.

[0018]According to one or more aspects of the invention, the UPS further
comprises a DC voltage source coupled to an inverter and wherein the
inverter is coupled to the AVR transformer and is configured to provide
regulated AC power to the AVR transformer. Also, according to one or more
aspects of the invention, the DC voltage source includes a battery.

[0019]According to one or more aspects of the invention, in a second mode
of operation, the core of the AVR transformer is coupled to the neutral
line and the at least one switch is selectively coupled to the core in a
configuration that results in the output voltage of the AVR transformer
being greater than the input voltage of the AVR transformer by a first
ratio.

[0020]According to one or more aspects of the invention, in a third mode
of operation, the core of the AVR transformer is coupled to the neutral
line and the at least one switch is selectively coupled to the core in a
configuration that results in the output voltage of the AVR transformer
to be greater than the input voltage of the AVR transformer by a second
ratio which is larger than the first ratio. Also, according to one or
more aspects of the invention, the second ratio is twice the first ratio.

[0021]According to one or more aspects of the invention, in a fourth mode
of operation, the core of the AVR transformer is coupled to the neutral
line and the at least one switch is selectively coupled to the core in a
configuration that results in the output voltage of the AVR transformer
being smaller than the input voltage of the AVR transformer.

BRIEF DESCRIPTION OF DRAWINGS

[0022]The accompanying drawings are not intended to be drawn to scale, in
the drawings, each identical or nearly identical component that is
illustrated in various figures is represented by a like numeral. For
purposes of clarity, not every component may be labeled in every drawing.
In the drawings:

[0023]FIG. 1 is a block diagram of a line interactive uninterruptible
power supply including an automatic voltage regulation transformer.

[0024]FIG. 2 is a schematic view of an automatic voltage regulation
transformer included in a UPS in accordance with the present invention.

[0025]FIG. 3 is a schematic view of an automatic voltage regulation
transformer in the inverter mode in accordance with the present
invention.

[0026]FIG. 4 is a schematic view of an automatic voltage regulation
transformer in the pass through mode in accordance with the present
invention.

[0027]FIG. 5 is a schematic view of an automatic voltage regulation
transformer in the boost mode in accordance with the present invention.

[0028]FIG. 6 is a schematic view of an automatic voltage regulation
transformer in the double boost mode in accordance with the present
invention.

[0029]FIG. 7 is a schematic view of an automatic voltage regulation
transformer in the trim mode in accordance with the present invention.

DETAILED DESCRIPTION

[0030]Embodiments of the invention are not limited to the details of
construction and the arrangement of components set forth in the following
description or illustrated in the drawings. Embodiments of the invention
are capable of being practiced or of being carried out in various ways.
Also, the phraseology and terminology used herein is for the purpose of
description and should not be regarded as limiting. The use of
"including," "comprising," or "having," "containing", "involving", and
variations thereof herein, is meant to encompass the items listed
thereafter and equivalents thereof as well as additional items.

[0031]A drawback of utilizing an AVR transformer to stabilize a voltage at
the output of a UPS is that an AVR transformer consumes energy even when
not regulating the output voltage, which leads to energy losses in the
transformer. In at least some embodiments of the present invention, the
problems associated with AVR transformer energy loss in a UPS are
eliminated by de-energizing the core of the transformer and preventing
losses due to the AVR transformer when the AVR is not regulating the
output voltage.

[0032]One embodiment of an uninterruptible power supply in accordance with
the present invention will now be described with reference to FIG. 1
which shows a block diagram of a line interactive uninterruptible power
supply (UPS) 10 for providing AC power to a load. The UPS includes an
input 12 to receive AC power from an AC power source, an output 14 that
provides AC power to at least one controlled outlet 13, a DC voltage
source 11 coupled to a DC to DC converter 15, an inverter 18 operatively
coupled to the DC to DC converter 15 to receive DC power and to provide
AC power, a transfer relay 16 selectively coupled to the UPS input 12 and
the inverter 18, a UPS controller 17, an external communication control
circuit 19 for communicating with external devices, an EMI/Surge filter
21, and an automatic voltage regulation (AVR) transformer 20 coupled to a
bypass relay 34, the transfer relay 16 and at least one AVR relay 43. The
DC voltage source 11 includes a battery 22, at least one backup battery
pack 23, a battery charger 25 and a logic supply 35. The UPS controller
17 is coupled to a current sense circuit 37, a voltage sense circuit 39,
a line sense circuit 41, a switch relay control 45 and at least one
controllable relay 47.

[0033]With reference to FIG. 2, which shows a schematic view of the
automatic voltage regulation transformer, the AVR transformer 20 includes
an input 24, an output 30, a core 32 including a top portion 49, a middle
portion 51 and a bottom portion 53, a first AVR relay 26 selectively
coupled between the input 24 and either the top portion 49 of the core 32
or a first tap 27 coupled to the bottom portion 53 of the core 32, a
second AVR relay 28 selectively coupled between the output 30 and either
the top portion 49 of the core 32 or a second tap 29 coupled to the
middle portion 51 of the core 32, and a bypass relay 34 for decoupling
the AVR transformer core 32 from a neutral line 36. The first AVR relay
26, the second AVR relay 28 and the bypass relay 34 may be single pole
double throw (SPDT) relays. The bypass relay 34 may also be a single pole
single throw (SPST) relay. A metal oxide varistor may also be coupled
across the bypass relay 34 to absorb energy when the bypass relay 34 is
opened.

[0034]The operation of the UPS 10 will now be described with reference to
FIGS. 1-7. With reference to FIGS. 1-2, the UPS controller 17 monitors
the status of the UPS 10 by reading the outputs of the voltage sense
circuit 39, the current sense circuit 37 and the line sense circuit 41.
In monitoring the outputs, the UPS controller may determine whether the
input voltage to the UPS 10 is in a normal or abnormal condition. The
input voltage is in an abnormal condition if the input voltage at the
input 12 of the UPS 10 is in a blackout, sag, or swell condition.
Irrespective of the input voltage, the UPS controller 17 operates the UPS
10 and the AVR transformer 20 so that the voltage at the output 30 is
within predetermined values, i.e. a nominal value plus or minus a given
threshold.

[0035]For example, with reference to FIGS. 1 and 3, if the input voltage
at the input 12 of the UPS 10 fails (blackout), the UPS controller 17
activates the transfer relay 16 to couple the AVR transformer 20 to the
inverter 18 to receive voltage from the DC voltage source 11 instead of
the input 12. DC power from the DC voltage source 11 is regulated by the
DC to DC converter 15, which is controlled by the UPS controller 17. The
regulated DC power from the DC/DC converter 15 is converted to AC power
by the inverter 18 and output to the transfer relay 16 and AVR
transformer 20. With reference to FIG. 3, which shows operation in
inverter mode, the UPS controller 17 adjusts the AVR relays 26, 28 to an
inverter mode in which the AVR transformer 20 is not required to perform
an output voltage regulation function. The AVR transformer is not
required to perform an output voltage regulation function because the DC
voltage from the DC voltage source 11 is already regulated by the DC/DC
converter 15 and DC/AC converter 18. In the pass through mode, the first
AVR relay 26 is set in a second position 48 and the second AVR relay 28
is set in a second position 44 with both AVR relays 26, 28 coupled to the
top portion 49 of the core 32 so that the taps 27, 29 are de-energized
and the voltage at the output 30 of the AVR transformer 20 is equal to
the voltage at the input 24 of the AVR transformer 20. Also, in the
inverter mode, the bypass relay 34 is opened to decouple the core 32 of
the AVR transformer from a neutral line 36 to eliminate any potential
losses due to the AVR transformer 20. The UPS controller also operates a
set of controllable relays 47, through a switch relay control 45, which
determine which controlled outlets 13 will be connected to the output 14.

[0036]In another example, with reference to FIGS. 1 and 4, if the input
voltage at the input 12 of the UPS 10 is at a normal level and AVR
transformer regulation is not required, the transfer relay 16 couples the
AVR transformer 20 to the input of the UPS 10 and the UPS controller 17
adjusts the AVR relays 26, 28 to a pass through mode in which the AVR
transformer 20 is not required to perform an output voltage regulation
function. In the pass through mode, the first AVR relay 26 is set in a
second position 48 and the second AVR 28 is set in a second position 44
with AVR relays 26, 28 coupled to the top portion 49 of the core 32, so
that the taps 27, 29 are de-energized and the voltage at the output 30 of
the AVR transformer 20 is equal to the voltage at the input 24 of the AVR
transformer 20. Also, in the pass through mode, the bypass relay 34 is
opened to decouple the core 32 of the AVR transformer from a neutral line
36 to eliminate any potential losses due to the AVR transformer 20.

[0037]If the input voltage is in a sag or swell condition, the transfer
relay 16 couples the AVR transformer 20 to the input of the UPS 10 and
the UPS controller 17 adjusts the AVR relays 26, 28, consequently
activating or deactivating the corresponding taps 27, 29 to provide a
stabilized voltage at the output 30 of the AVR transformer.

[0038]For example, with reference to FIG. 5, if the input voltage at the
input 12 of the UPS 10 is in a sag condition and the output voltage needs
to be increased, the UPS controller 17 adjusts the AVR relays 26, 28 to a
boost mode. In the boost mode, the first AVR relay 26 of the AVR
transformer 20, is set in a first position 38, coupled to the bottom
portion 53 of the core 32, so that the first tap 27 is energized and the
second AVR relay 28 of the AVR transformer 20 is set in a first position
40, coupled to the middle portion 51 of the core 32, so that the second
tap 29 is energized, allowing the electrical current 42 at the input 24
of the AVR transformer 20 to flow from the bottom portion 53 of the core
32 to the middle portion 51 of the core in a first direction, resulting
in the voltage at the output 30 of the AVR transformer 20 being greater
than the voltage at the input 24 of the AVR transformer 20. The increase
of voltage between the output 30 and input 24 due to the AVR transformer
20 is directly correlated to the turn ratio of the core 32 of the AVR
transformer 20 which varies depending on where the core 32 is tapped
(determined by the first and second AVR relays 26, 28 and corresponding
taps 27, 29 of the AVR transformer 20). For example, in the boost mode,
the voltage at the output of the AVR transformer may be increased, in
relation to the voltage at the input of the AVR transformer, by a first
ratio. The first ratio may be 1:1.15.

[0039]With reference to FIG. 6, if the output voltage needs to be
increased by a greater ratio, the second AVR relay 28 of the AVR
transformer 20, can be put in a second position 44, coupled to the top
portion 49 of the core 32, so that the second tap 29 is de-energized,
allowing the current 46 to flow through a larger portion of the core 32,
from the bottom portion 53 to the top portion 49, in the first direction,
effectively increasing the turn ratio of the AVR transformer, and
resulting in a larger voltage at the output 30. For example, in the boost
mode, the voltage at the output of the AVR transformer may be increased
by a second ratio which is greater than the first ratio. In one
embodiment, the second ratio may be double the value of the first ratio.
The second ratio may be 1:1.3.

[0040]In another example, with reference to FIG. 7, if the input voltage
at the input 12 of the UPS 10 is in an swell condition and the output
voltage needs to be reduced, the transfer relay 16 couples the AVR
transformer 20 to the input of the UPS 10 and the UPS controller 17
adjusts the AVR relays 26, 28 to a trim mode. In the trim mode, the first
AVR relay 26 of the AVR transformer 20, is set in a second position 48,
coupled to the top portion 49 of the core 32, so that the first tap 27 is
de-energized, and the second AVR relay 28 of the AVR transformer 20, is
set in a first position 40, coupled to the middle portion 51 of the core
32, so that the second tap 29 is energized, allowing the electrical
current 50 at the input 24 of the AVR transformer 20 to flow through a
section of the core 52 of the AVR transformer, from the top portion 49 to
the middle portion 51, in a second direction, which results in the
voltage at the output 30 of the AVR transformer 20 being lower than the
voltage at the input 24 of the AVR transformer 20. The decrease of
voltage between the output 30 and input 24 due to the AVR transformer 20
is directly correlated to the turn ratio of the core 32 of the AVR
transformer 20. For example, in the trim mode, the voltage at the output
of the AVR transformer may be decreased, in relation to the voltage at
the input of the AVR transformer, by a ratio. The ratio may be 1.15:1.

[0041]When the AVR transformer core is transitioned from an energized to
de-energized state or from a de-energized state to an energized state, it
is beneficial in at least one embodiment to operate the AVR relays of the
AVR transformer and the bypass relay in such a way to minimize any loss
of volt-seconds or imbalance in the UPS. For example, in at least one
embodiment the UPS controller 17 engages the bypass relay as close to the
zero crossing of the AC voltage waveform as possible to minimize any loss
of volt-seconds. Additionally, in at least one embodiment the UPS
controllers 17 engages the bypass relays and the AVR relays exactly 180
degree apart to minimize any loss of volt-seconds or imbalance. For
example, when the AVR transformer core is transitioned from a
de-energized to an energized state, the bypass relay may be engaged
first, followed by the AVR relays exactly one half cycle later. In
another example, when the AVR transformer is transitioned from an
energized to a de-energized state, the AVR relays may be engaged first,
followed by the bypass relay exactly one half cycle later.

[0042]One advantage to at least one embodiment of the present invention
described above is that the problems usually associated with AVR
transformer energy loss in a UPS are reduced by de-energizing the core of
the transformer and preventing losses due to the AVR transformer when the
AVR is not performing a regulation function. By de-energizing the core,
electric current is prevented from flowing in the core, which results in
the elimination of any tare loss due to the AVR transformer when the ACR
transformer is not performing a regulation function.

[0043]Embodiments of the invention are described above in conjunction with
a line interactive UPS. The methods and systems described herein can also
be used with other types of uninterruptible power supplies and in a
variety of power supply systems and voltage regulation systems.

[0044]As described above, the systems and methods of embodiments of the
invention utilize a plurality of different switches. The switches could
be implemented in a variety of different ways such as, but not limited
to, SPDT relays, SPST relays, transistors or other types of switches.

[0045]In at least one embodiment, the DC voltage supply 11 includes extra
battery packs 23 to provide extra DC storage capacity, a battery charger
for converting AC voltage from the input 12 into DC voltage to charge the
battery 22 and backup battery packs 23, and a logic supply 21 for
providing regulated DC voltages. In other embodiments, other backup power
sources may be used including AC and DC generators.

[0046]In at least one embodiment the UPS controller 17 is connected to an
external communication control circuit 19 to communicate with external
devices.

[0047]In at least one embodiment the input 12 is connected to an EMI/Surge
filter 21 to provide EMI and surge protection to the UPS 10.

[0048]In at least one embodiment, the controllable relays 47 are not
included in the UPS and the controlled outlets 13 are not controlled
outlets but are standard outlets.

[0049]As described above, the systems and methods of embodiments of the
invention utilize a UPS controller. The UPS controller could be
implemented in a variety of different ways such as, but not limited to, a
microprocessor, logic circuit, computer or other type of electronic
controller.

[0050]Having thus described several aspects of at least one embodiment of
this invention, it is to be appreciated various alterations,
modifications, and improvements will readily occur to those skilled in
the art. Such alterations, modifications, and improvements are intended
to be part of this disclosure, and are intended to be within the spirit
and scope of the invention. Accordingly, the foregoing description and
drawings are by way of example only.